The present invention pertains generally to surgical and diagnostic systems that use light as the operative medium. More particularly, the present invention pertains to light beam delivery systems, and methods for their use, which generate aberration-free light beams that are useful for ophthalmologic purposes. The present invention is particularly, but not exclusively, useful for incorporating an active mirror into a light delivery system for the purpose of generating an aberration-free light beam.
Whenever an object is to be measured, evaluated or somehow modified, it is absolutely necessary that some base reference be established from which the precision and accuracy of the accomplished task can be determined. In order to do this, for some applications it is necessary that the system, device or apparatus being used, be able to accurately and reliably establish its own base reference.
In the field of ophthalmology, the systems that are used for generating surgical light beams, or for making optical measurements, are, in general, extremely sensitive and extraordinarily susceptible to environmental changes. For instance, in addition to the more obvious perturbations and disturbances that may be caused by physically jostling optical equipment, the temperature and humidity conditions in the operational environment may also cause these optical systems to fall out of alignment (i.e. move away from the base reference). Consequently, in order to maintain their accuracy and reliability during an operation, optical systems should be capable of adapting to dynamic changes, as well as being statically stable. Further, in addition to the environmental factors that can affect the operation of an optical system, the physical components of an optical system (e.g. lenses, mirrors, filters and beam splitters) can also affect the operation. This will be so for all applications, under any condition. Still further, there are applications wherein the aberrations that are contributed by the optical specimen may also be important and need to be accounted for (e.g. retinal surgery). In any event, the specific instance wherein wavefront analysis techniques are to be employed, the ability of an optical system to accurately establish and precisely maintain its base reference is critical.
Wavefront analysis techniques rely on the notion that the individual component rays of a light beam will speed up or slow down at different rates according to their refractive history. For wavefront analysis, a plane wavefront, i.e. one wherein all of the individual component rays of light arrive at a same distance from their common source at the same time, serves as a useful and identifiable base reference. Thus, if a light beam is known or is established to have a plane wavefront, any perturbations or disturbances to the light beam will introduce aberrations which cause the wavefront of the light beam to become somehow distorted. Recently, it has been possible to effectively measure such distortions using devices such as a Hartmann-Shack sensor.
As indicated above, for specific applications wherein the purpose of a light beam delivery system needs to account for the optical characteristics of a specimen, such as an eye, it is desirable to isolate the optical aberrations that are introduced by the specimen. As mentioned above, these aberrations will manifest themselves as changes in the wavefront of the light beam that has passed through the specimen. Accordingly, if changes in the wavefront that result when light passes through the specimen can be determined, the optical characteristics of the specimen can also be determined. This, of course, requires the changes in the wavefront be measured. A convenient base reference for these purposes is a plane wavefront, or some other definable and ascertainable wavefront.
In light of the above, it is an object of the present invention to provide a light delivery system for use in evaluating an optical specimen, that effectively generates an aberration-free wavefront for the light beam as it is incident on the specimen, or after it has passed through the specimen. Another object of the present invention is to provide a light beam delivery system that employs a programmable active mirror, for generating an aberration-free light beam that can be subsequently used for surgical or diagnostic purposes. Still another object of the present invention is to provide a light beam delivery system that maintains an essentially aberration-free light beam despite dynamic changes in the environmental factors that would otherwise affect the optical alignment of the system. Another object of the present invention is to provide a light beam delivery system that will optically isolate a specimen so that it can be evaluated free of interfering distortions from other sources. Yet another object of the present invention is to provide a light beam delivery system that is relatively easy to manufacture, is simple to use, and is comparatively cost effective.
In accordance with the present invention, a device and method for establishing an aberration-free delivery system for use in evaluating, altering or modifying an optical specimen envisions accounting for optical aberration in a two step process. The first step involves compensating for those optical aberrations that are introduced by the delivery system. The second step, if necessary or desired, involves compensating for the optical aberrations that are introduced by the optical specimen itself.
In detail, the delivery system of the present invention includes a light source. Specifically, the light source directs a light beam through the delivery system and toward the specimen. More specifically, after passing through the delivery system, the light beam is directed along a beam path toward an active mirror and it is then reflected from the active mirror toward the specimen. Included are a first beam splitter and a second beam splitter that are sequentially positioned on the beam path between the active mirror and the specimen. The purpose of the first beam splitter is to direct about ten percent of the light that is reflected from the active mirror toward a detector before this light is incident on the specimen. Importantly, however, this happens after the light has passed through the delivery system. On the other hand, the purpose of the second beam splitter is to direct light that is subsequently reflected from the optical specimen toward the detector. For the present invention, the detector is preferably a device such as a Hartmann-Shack sensor.
In the first operational step for the present invention, the light that is reflected toward the detector by the first beam splitter will be characterized by a first wavefront. The important consideration here is that this first wavefront includes all of the aberrations that were introduced into the light beam as it passed through the delivery system. A computer/comparator then compares this first wavefront with a base reference (e.g. a plane wavefront), and generates a signal(s) which is indicative of the difference between the first wavefront and the base reference. This signal is then used to program the active mirror so that, in the first operation step, the light reflected toward the specimen from the active mirror will be an essentially aberration-free light beam.
For applications wherein the objective is to generate only a plane wavefront, the second step of the present invention can be omitted. However, if the optical aberrations that are contributed by the specimen are also required, such as for retinal surgery, the present invention envisions an evaluation of the optical specimen in the second step.
In the second step, as a result of implementing the first step, a plane wavefront is reflected from the active mirror and is directed toward the specimen. As this light is reflected from the specimen it will have a second wavefront which is indicative of only the optical aberrations that are contributed by the specimen. The second beam splitter then directs this second wavefront toward the detector. Next, the computer/comparator compares the second wavefront with a base reference (e.g. a plane wavefront), and generates a signal(s) which is indicative of the difference between the second wavefront and the base reference. This signal can then be used to program the active mirror so that light reflected from the active mirror toward the specimen will be a negative of the aberration contribution from the optical specimen. This negative will then cancel the aberration contribution of the optical specimen and the result will be an essentially aberration-free light beam.
In accordance with the present invention, by implementing only the first step, the system can use closed-loop control of the active mirror to maintain the first wavefront as an aberration-free, plane wavefront. Thus, corrections to this first wavefront can be continuously pre-programmed into the active mirror (i.e. continuous closed-loop control). Alternatively, when both steps are implemented, closed-loop control of the active mirror can be accomplished to establish the second wavefront as desired. In this case, the first step can be periodically made at predetermined time intervals (i.e. a hybrid open/closed-loop control) to account for changes in the optical aberration contribution of the delivery system.
As will be appreciated by the skilled artisan, the second wavefront can be analyzed by the computer/comparator to evaluate the optical specimen for surgical or diagnostic purposes. Further, as envisioned by the present invention, the light that is used for programming the active mirror, and the light that is used to surgically alter or modify the optical specimen, can have different wavelengths.